Third and fourth generation mobile telecommunication systems, such as those based on the 3GPP defined UMTS and Long Term Evolution (LTE) architecture are able to support more sophisticated services than simple voice and messaging services offered by previous generations of mobile telecommunication systems.
For example, with the improved radio interface and enhanced data rates provided by LTE systems, a user is able to enjoy high data rate applications such as mobile video streaming and mobile video conferencing that would previously only have been available via a fixed line data connection. The demand to deploy third and fourth generation networks is therefore strong and the coverage area of these networks, i.e. geographic locations where access to the networks is possible, is expected to increase rapidly.
The anticipated widespread deployment of third and fourth generation networks has led to the parallel development of a class of devices and applications which, rather than taking advantage of the high data rates available, instead take advantage of the robust radio interface and increasing ubiquity of the coverage area. Examples include so-called machine type communication (MTC) applications, which are typified by semi-autonomous or autonomous wireless communication devices (i.e. MTC devices) communicating small amounts of data on a relatively infrequent basis. Examples include so-called smart meters which, for example, are located in a customer's house and periodically transmit information back to a central MTC server data relating to the customers consumption of a utility such as gas, water, electricity and so on. Other examples include medical devices which are continuously or intermittently transmitting data such as for example measurements or readings from monitors via a communications network to a server, and automotive applications in which measurement data is gathered from sensors on a vehicle and transmitted via a mobile communications network to a server attached to the network.
Whilst it can be convenient for a terminal such as an MTC type terminal to take advantage of the wide coverage area provided by a third or fourth generation mobile telecommunication network, there are at present disadvantages and challenges to successful deployment. Unlike a conventional third or fourth generation terminal device such as a smartphone, an MTC-type terminal is preferably relatively simple and inexpensive, having a reduced capability. In addition MTC-devices are often deployed in situations that do not afford easy access for direct maintenance or replacement, so that reliable and efficient operation can be crucial. Furthermore, while the type of functions performed by the MTC-type terminal (e.g. collecting and reporting back data) do not require particularly complex processing to perform, third and fourth generation mobile telecommunication networks typically employ advanced data modulation techniques (such as 16QAM or 64QAM) on the radio interface which can require more complex and expensive radio transceivers to implement.
It is usually justified to include such complex transceivers in a smartphone as a smartphone will typically require a powerful processor to perform typical smartphone type functions. However, as indicated above, there is now a desire to use relatively inexpensive and less complex devices to communicate using LTE type networks. In parallel with this drive to provide network accessibility to devices having different operational functionality, e.g. reduced bandwidth operation, there is a desire to optimise the use of the available bandwidth in a telecommunications system supporting such devices. Accordingly it has been proposed to provide a so called “virtual carrier” within the host carrier bandwidth of an LTE network, which provides communications resources for preferable allocation to MTC-type devices, which are referred to interchangeably in the following description as VC-UEs. A virtual carrier is therefore tailored to low capability terminals such as MTC devices and is thus provided within the transmission resources of at least the conventional OFDM type downlink carrier (i.e. a “host carrier”). Unlike data transmitted on a conventional OFDM type downlink carrier, data transmitted on the virtual carrier can be received and decoded without needing to process the full bandwidth of the downlink host OFDM carrier, for at least some part of a sub-frame. Accordingly, data transmitted on the virtual carrier can be received and decoded using a reduced complexity receiver unit.
The term “virtual carrier” corresponds in essence to a narrowband carrier for MTC-type devices within a host carrier for an OFDM-based radio access technology (such as WiMAX or LTE).
The virtual carrier concept is described in a number of co-pending patent applications (including GB 1101970.0 [2], GB 1101981.7 [3], GB 1101966.8 [4], GB 1101983.3 [5], GB 1101853.8 [6], GB 1101982.5 [7], GB 1101980.9 [8] and GB 1101972.6 [9]), the contents of which are incorporated herein by reference.
In order to deploy a virtual carrier for access by communications devices such as MTC devices some adaptation of existing signalling and messages may be required, but as far as possible without adapting the host mobile communications network so as to provide compatibility with conventional communications devices.